Method for accelerated aerobic decomposition of vegetative organic waste material

ABSTRACT

A method for aerobic decomposition of vegetative organic waste material including high flow-rate aeration, compaction of the organic material, and continual percolation of moisture released therefrom in a collapsible, portable, bag container to provide beneficial soil amendments, fertilizers, and supplemental heat sources.

RELATED APPLICATION

This application is a continuation of copending U.S. patent applicationSer. No. 07/738,958, filed on Aug. 1, 1991 and now abandoned.

FIELD OF THE INVENTION

This invention is related generally to the aerobic decomposition ofvegetative organic waste material and, more particularly, to a methodand apparatus used therewith to greatly accelerate such decomposition.

BACKGROUND OF THE INVENTION

The past several years have been witness to a renewed interest in theenvironment. The special attention afforded so-called "green" productsand methods of production attest to the fact that commercial viabilityis not always contrary to resource conservation. Often, environmentalregulations and/or restrictions provide the impetus for innovativemethods and apparatus.

A case in point is the recent legislative trend toward banning landfilldisposal of various waste materials. Of course, many hazardous chemicaland biological wastes have long been restricted, but with availablelandfill space becoming increasingly scarce, common yard and variousrelated forms of vegetative organic wastes will soon require alternatemeans of disposal. Municipalities and other levels of government arefaced with an urgent and growing problem.

The advantages of composting or decomposing organic material to providevarious fertilizers and/or soil amendments are well-known. The challengehas always been one of adapting backyard garden techniques to processescapable of handling large volumes, such as those typically generated bymunicipalities, in a safe, environmentally-conscious manner. The problemhas been compounded in recent years by the budgetary constraints underwhich most governmental units operate. Economy and fiscal responsibilityare, thus, additional on-going concerns in the art.

The prior art includes a variety of attempts to produce an apparatus orderive a method to decompose or compost waste organic material throughthe metabolic activity of aerobic bacteria. Most provide only limitedsuccess. U.S. Pat. No. 3,934,999 describes use of an aqueous bacterialinoculant and depends on absorption of solar heat to decompose a smallamount of dry organic material placed in a common home garbage bag. Anumber of evenly spaced apertures in the bag allow passive movement ofair and facilitate composting. Periodic, manual agitation of material isrequired and possible only because the method is restricted toexceedingly small volumes.

U.S. Pat. No. 3,756,784 is directed to a complex apparatus for thesequential composting of domestic refuse and includes a plurality ofessentially immovable vertically-disposed chambers, each with its ownagitator, water supply, and air supply. The rates of addition of air andwater are a function of temperature and carbon dioxide levels in eachchamber. A varying combination of air, water, and agitation must beaccurately administered to maintain aerobic conditions in each chamber.

U.S. Pat. No. 4,302,546 discloses a constantly rotating tank-likeapparatus to recycle animal wastes. Carbonaceous filler materials mustbe added to control moisture content. Continual, low flow-rate aerationfacilitates decomposition. Exhaust air is past through a scrubber toeliminate foul-smelling components which would otherwise pollute thesurrounding atmosphere.

U.S. Pat. Nos. 3,138,447 and 3,930,799 are directed to a process andapparatus, respectively, for producing fertilizer from organic andinorganic municipal garbage. Low flow-rate aeration is aided by constant"tumbling" to prevent air channel formation. Moisture is firstintroduced to enhance decomposition via the addition of sewerage sludgethen removed during a later drying phase. Temperature and carbon dioxidelevels are monitored throughout decomposition.

U.S. Pat. No. 4,230,676 describes an apparatus and method fordecomposition using exposed windrows of organic material. Integral toboth the apparatus and method is a microprocessor which monitorstemperature, air/moisture content, and pH of the windrowed material. Acomplex, adjustable injector configuration makes anyadditions/corrections necessary in response thereto.

Various prior art sources teach the use of a Beltsville or modifiedBeltsville system, which is necessarily limited to composting smallvolumes of material under tropic or warm weather conditions through useof a solar forced-air collector. Low-rate aeration and initial additionof water to loosely-arranged material characterize methods of this type.The apparatus used therewith typically includes overlapping sheets ofplastic to catch rain water.

These are but a few examples of the prior art. Other methods and/orapparatus may be characterized as involving extensive waste analysis andmonitoring, supplemental heat supplies, and agitation, among other stepsor components. As is evident, a considerable number of drawbacks andproblems exist in the prior art relating to the beneficial decompositionof organic waste materials.

There is a need for an improved aerobic decomposition method to morefully utilize the advantages associated with re-using waste materials ofthe sort and, at the same time, provide for a feasible,environmentally-safe alternative to landfill disposal.

OBJECTS OF THE INVENTION

It is an object of this invention to provide a method of accelerateddecomposition of vegetative organic waste material, overcoming some ofthe problems and shortcomings of the prior art, including thosementioned above.

Another object of this invention is to provide a method for quick,efficient decomposition of large volumes of vegetative organic materialas a useful alternative for landfill disposal.

Another object of this invention is to provide a method of decompositionwhich may be used with large volumes of organic material in conjunctionwith a light-weight, portable apparatus.

Another object of this invention is to provide a method of decompositionwhich does not require the use of a complex, expensive apparatuscomprising numerous constantly-moving components prone to costly repairand maintenance.

Another object of this invention is to provide a method of decompositionsuch that the desired degree of bacterial degradation may be achievedwithout resort to complex and/or computerized analytic techniques.

Another object of this invention is to provide an odor-free method ofdecomposition without use of pollution-control or abatement devices.

Another object of this invention is to provide a method of decompositionwhich does not necessitate either a chemical or bacterial inoculant oran extraneous heat source such as solar radiation.

Another object of this invention is to provide a method of decompositionwhich does require the use of either dry, absorptive filler materials orsewage sludge to obtain suitable moisture levels.

These and other important objects will be apparent from the descriptionsof this invention which follow.

SUMMARY OF THE INVENTION

This invention is a method for accelerated decomposition of largevolumes of vegetative organic waste material. It overcomes certainwell-known problems and deficiencies, including those outlined above. Animportant aspect of this invention is a novel combination of constanthigh-flow rate aeration, material compaction, and continual moisturepercolation, all of which are used in conjunction with a uniquecontainer apparatus to provide not only a viable alternative to landfilldisposal, but means to produce useful soil amendments, fertilizers, anda source of supplemental heat. The inventive method allows for quick,cost-effective aerobic decomposition, such that the advantagesassociated with recycling materials of this sort may be more fullyrealized.

This invention is a method of aerobically decomposing large volumes ofvegetative organic material including (1) providing a substantiallycollapsible or portable container having at least one open end, ventmeans, and an upper portion with a plurality of openings, said containerconnected at said openings to means for variable high-rate air intake;(2) packing the container with vegetative organic material having amoisture content; (3) closing the open end of the container such that itis substantially moisture-retentive; (4) aerating the containercontinuously through the openings at a rate of about 200-1500 cubic feetper minute; and (5) percolating moisture throughout the organicmaterial.

In preferred embodiments of this invention, the container is a flexible,substantially moisture-impermeable bag; and the air-intake means is adischarge blower connected to a series of conduits such that theconduits are inserted through the container openings and extendsubstantially to the bottom of the bag. In highly preferred embodiments,the conduits are perforated in those portions extending into the bag.

In preferred embodiments of this invention, the organic material isaerated at a rate of about 400-1100 cubic feet per minute and a staticpressure of at least 0.5 inches of water. In highly preferredembodiments, the organic material is aerated at a rate of about 600cubic feet per minute and a static pressure of about 0.5-1.5 inches ofwater.

The organic material decomposed through the method of this inventionpreferably includes a bulking agent in about 10-75% by weight of theorganic material. In highly preferred embodiments, the weight of thebulking agent is about 25-50% of the total weight of the organicmaterial.

In preferred embodiments of this invention, the organic material ispacked into the bag with a pressure of about 0.1-10.0 pounds per squareinch. In preferred embodiments, the packing pressure is about 0.5-5.0pounds per square inch, such that the packed material has a density ofabout 10-75 pounds per cubic foot. In highly preferred embodiments, thepacked material has a density of about 25-35 pounds per cubic foot suchthat it retains heat generated during composition yet allows movement ofmoisture of air therethrough.

As a final step, this method includes percolation whereby moisturecontent is released from the organic material during composition, thenvaporized by heat generated and condensed on the container.

The method of this invention also contemplates monitoring the internaltemperature of the organic material to determine the aeration raterequired for optimal decomposition. Likewise, the method may alsoinclude injecting water into the organic material to achieve optimaldecomposition.

As previously noted, the method of decomposition as revealed throughthis invention, has certain advantages, most of which relate directly tothe ease and rate at which a useful degree of decomposition may beachieved. Natural composting requires up to two years under typicalconditions. This inventive method permits large-scale decomposition in afraction of that time, such that volumes approximating 1,000 cubic yardsof waste may be sufficiently decomposed within four months or less witha concomitant volume reduction of nearly 80%.

Conservative estimates indicate a typical city of 750,000 may produce,won an average annual basis, 45,000 tons of yard and relatedwaste--waste which would otherwise be landfilled. When considered withthe fact useful by-products and a supplemental heat source may bederived from what would otherwise be a costly refuse problem, thebenefits available through use of this method to municipal governments,as well as others similarily-situated, are immediately evident.

As detailed more fully below, aerobic bacterial decomposition is a veryexothermic process. Temperatures exceeding 130° F. are typicallygenerated. As such, the high flow-rate aeration component of thisinventive method may be used to provide a supplemental heat source for avariety of functions, including the winter-heating of a greenhouse orsimilar such structure in which case the organic material decomposed isthat produced during the growing season.

Regardless, the material remaining upon completion of decomposition is auseful soil amendment and fertilizer for residential or agricultural usein that it provides excellent aeration and water-retention qualities andnutrients to any soil to which it is introduced. It may also be used inconjunction with various road and highway projects to prevent surfaceerosion.

Unlike methods of the prior art, that revealed herein may be employedwithout an expensive and complex apparatus. The preferred bag containerused in conjunction with this method is relatively inexpensive. It maybe used to decompose large volumes of organic waste material, yet may bepurchased at a fraction of the cost of conventional equipment. Costlyrepair and down-time associated with apparatus of the prior art areavoided by an absence of components moving against the weight of a largevolume of waste material. Furthermore, it is light-weight and portablesuch that it may be relocated once decomposition is complete.

As significant as these attributes are, perhaps the most importantbenefits derived from use of the bag apparatus of this invention arethose more directly related to the environment. The preferred bagcontainer eliminates wind-borne debris and preventspotentially-hazardous decomposition leachates from running into andcontaminating surface water. Together with odorless decomposition, theseadvantages make use of this method ideal for municipalities compostingnear residential areas.

The preferred discharge blower component effects high flow-rate aerationand is a useful compliment to the preferred bag container. Light weightand simplicity of design promote easy assembly and allow both the blowerand conduits to be moved with the preferred bag when or as needed.

Low cost and maintenance are important advantages associated with use ofthe preferred apparatus of this invention. Likewise, the water injectorand temperature monitoring means which may be used with the method ofthis invention are also effective without significantly increasing thecost of decomposition, an important consideration to municipalities andothers restrained by budget limitations.

Aerobic decomposition is predominantly a function of the internaltemperature of the waste material and aerobic bacteria indigenous to it,and proceeds effectively at a temperature of about 130°-160° F. As arule, when the temperature drops below this range bacterial activitydeclines; excessive heat promotes anaerobic decomposition. An inventiveaspect of this method includes control of decomposition through rate ofaeration. It has been established that changes in aeration rates may beused to effect almost-immediate response in mass temperature. As aresult, the internal temperature of the decomposing material be adjustedto within 5° F. of the desired temperature condition without resortingto expensive, complex microprocessors or other analytic methods of theprior art.

The need for complete aerobic decomposition is immediately obvious oncethe internal temperature of the organic mass exceeds the desired rangefor any length of time. The gaseous by-products of anaerobicdecomposition tend to be foul-smelling and are widely-considered a formof pollution completely unacceptable to those unfortunate to reside inclose proximity. The method of this invention prevents anaerobicbacterial activity such that decomposition proceeds effectively withoutoffensive odors or the need for auxiliary scrubbing or control devices.

As inferred above, bacteria indigenous to the waste material may beutilized without adding extraneous decomposition-enhancing chemicals orbacterial cultures. Inasmuch as inoculants of this sort are relativelyexpensive and require additional monitoring, a considerable cost-savingscompared to methods of the prior art may be realized.

This inventive method anticipates the possibility that the addition ofmoisture may be required to enhance the rate of decomposition withcertain extremely dry waste materials. However, with most organicwastes, the natural moisture content has been found sufficient,foregoing the need to add sewerage sludges or other high-water-contentmaterials which may have a corrosive, deleterious effect on anyapparatus used. Conversely, too much water does not impede this method.Because excessive moisture only enhances percolation and decomposition,filler materials of the prior art are not needed to absorb water.

The method of this invention would not seem appropriate for the aerobicdecomposition of organic material. Aeration systems of the prior artstress the use of low flow-rates in combination with loosely-arrangedwaste material either constantly or periodically agitated to encourageaerobic conditions. The use of high flow-rate aeration with compactedmaterial and continual percolation of moisture is contrary to the art,and the excellent results obtained were quite unexpected.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of an apparatus suitable for employing the methodof this invention is shown in the accompanying drawings, of which:

FIG. 1 is a sectional view of the apparatus;

FIG. 2 is a top view of the apparatus; and

FIG. 3 is a side view of the apparatus.

DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

The drawings illustrate the preferred embodiment of an apparatus whichmay be used to employ the method of this invention. The apparatusincludes bag 10 and air conduit 16 attached to blower 20.

As best shown in FIG. 1, bag 10 is provided with a plurality ofsubstantially evenly-spaced openings 14 through which air conduits 16are inserted. Joints 18 allow conduits 16 to be used in a seriesconfiguration. Once bag 10 is sufficiently packed with organic wastematerial, fastener means 12 secures the open end, creating asubstantially moisture-retentive container.

Air conduits 16 are connected to discharge blower 20 which, when inoperation, provides high flow-rate aeration throughout bag 10. Conduits16 extend substantially the depth of bag 10. Perforations 22 spacedalong conduits 16 allow air forced therethrough to permeate thevegetative matter. Homeostatic air flow is achieved throughincorporation of exhaust vents 24, preferably located in the upperportion of bag 10 between conduits 16. Temperature monitoring means mayalso be used in conjunction with the method of this invention. In suchcase, apertures 26, as shown in FIG. 1, are made through bag 10 forinsertion of such means into the material mass.

As best shown in FIGS. 2 and 3, water injection means 28 may be employedwith the method of this invention. If so, such means may be insertedthrough holes 30 into an upper portion of bag 10 and the vegetativematter contained therein. Preferably, injection means 28 is in a seriesconfiguration such that it is aligned between and at right angles toconduits 16.

High flow-rate aeration and an apparatus to provide the same areessential to the aerobic decomposition described herein. In accordancewith this invention, a container packed with vegetative organic materialis aerated continuously at a rate of about 200-1500 cubic feet perminute to obtain optimal aerobic decomposition conditions. At aerationrates below this range, anaerobic bacteria and odiferous metabolicby-products predominate; aeration in excess of this rate appears tocreate conditions disruptive to aerobic bacterial activity.

In preferred embodiments of this invention, air is forced through acontainer apparatus at a rate of about 400-1100 cubic feet per minute.In highly preferred embodiments, accelerated decomposition may beachieved with a flow rate of about 600 cubic feet per minute. Air flowmust be conducted at a sufficient static pressure to achieve the desiredaerobic decomposition. Pressures of at least 0.5 inches of water areneeded to force the preferred volumes of air through the air conduits.Studies show that pressures of 0.5-1.5 inches of water provide excellentresults.

Bulking agents such as straw, wood chips, and the like may be used withthe method of this invention. Inclusion of these materials promoteaeration and enhance aerobic decomposition by creating air spaces andpassages within the vegetative mass. As a result, optimal aerobictemperatures may be obtained more readily and adjusted by air-flow ratesmore efficiently.

As stated above, a bulking agent may comprise about 10-70 percent byweight of the vegetative organic material to be decomposed. The exactamount utilized depends, in large part, on the compaction susceptibilityof the vegetative material which, in turn, depends upon its moisturecontent. It has been found with most waste materials the bulking agentshould be about 25-50 percent of the total weight of the organicmaterial. The exact amount used may vary with the air flow-rateutilized.

It is essential that the organic material be compacted into thecontainer apparatus to retain heat generated during decomposition andfurther enhance aerobic bacterial activity. Unlike methods of the priorart, most of which include means to prevent compaction, a preferredmethod of this invention entails filling a container with moderatepressure. The pressure utilized varies and depends, in part, on themoisture content of the material to be decomposed.

Typically, pressures of about 0.5-5.0 pounds per square inch areemployed during packing process. With materials such as grasses whichhave a relatively high moisture content, the pressure used will tendtoward the lower end of this range; higher pressures will result in amass density which may preclude sufficient aeration and lead to unwantedanaerobic decomposition. Conversely, materials such as dry leaves arepacked with pressures near the upper end of the aforementioned range. Inthese situations, too little pressure results in a material mass withinsufficient heat retention qualities. To some degree, packing pressuresmay be modified for a given material and moisture content throughadjustment of the amount of bulking agent used. Packing may beaccomplished through use of apparatus well-known to those made familiarwith this invention. Blowers and auger-type devices which supplysufficient, constant pressures of the sort described herein may besuccessfully.

Constant high flow-rate aeration is accompanied by continual percolationof moisture throughout the material mass. The preferred bag containerused in conjunction with this inventive method permits accumulation ofmoisture as it is released from the decomposing material. Asdecomposition proceeds, the internal temperature rises and the releasedmoisture vaporizes, passing through the material and condensing on thesurface of the bag container. The combination of repeated percolation ofmoisture and high flow-rate aeration enhances aerobic bacterial activityand accelerates decomposition.

To decompose of especially dry vegetative material, the method of thisinvention contemplates initial injection of water to approximate asuitable moisture content equivalent to about 20-65% of the weight ofthe material. Typically, only one such injection is required as themoisture is thereafter continually recycled through the percolation stepdescribed above.

Preferred bag 10 may be made using a variety of materials, includingpolyethylene and other similar durable, flexible plastics. Any materialutilized must resist tears when openings are introduced as exhaust ventsor for the insertion of aeration conduits, yet must be flexible andextendable enough to accommodate the collection of a significant amountof moisture once decomposition begins. It has been found that apolyethylene bag with a thickness in excess of 6 mil provides excellentresults under the decomposition conditions employed with this method.Thinner materials do not provide the strength and flexibility needed toprocess large volumes of waste material.

Preferred polyethylene bags may range from 10-250 feet in length. Forvolumes effectively decomposed through use of this method, a 100-footbag provides excellent results. Such containers are available fromsources well known to those skilled in the art and include AG-BAGCorporation of Warrenton, Oreg., among others.

Blower 20 and conduits 16 may also be obtained from a variety of sourceswell-known to those made aware of this invention. In particular,excellent results will be obtained through use of a blower with means tovary flow-rates such that internal mass temperatures may be adjusted asneeded to provide optimal decomposition conditions. One such blower,suitable for employing the method of this invention, is available fromDayton Electric Manufacturing Company of Chicago, Ill.

While the principles of this invention have been described in connectionwith specific embodiments, it should be understood clearly that thesedescriptions are made only by way of example and are not intended tolimit the scope of the invention. For example, the container apparatusused in conjunction with this method may include various mesh-typematerials which permit retention of heat and allow condensation ofinternal moisture. Likewise, vegetative materials are not necessarilylimited to the yard and related waste described. Waste paper, lakealgae, and a variety of other vegetative organic materials are suitablefor decomposition through the method of this invention.

I claim:
 1. A method for aerobically decomposing large volumes ofvegetative organic material, comprising:providing a substantiallycollapsible, moisture-retentive, and portable container having at leastone open end and an upper portion with a plurality of openings, saidcontainer connected at said openings to means for variable high-rate airintake and vent means comprising a plurality of aperatures sufficient innumber and dimension to maintain homeostatic airflow and aerobicdecomposition temperatures; packing the container with vegetativeorganic material having a releasible moisture content at pressure ofabout 0.1-10.0 pounds per square inch, whereby the organic material hasa density of about 10-75 pounds per cubic foot such that said materialis substantially heat retentive, permits movement of moisturetherethrough, and maintains homeostatic airflow and aerobicdecomposition temperatures; closing the open end of the container suchthat said container is substantially moisture-retentive; aerating thecontainer substantially continuously through said openings at a rate ofabout 200-1500 cubic feet per minute to control and maintain sufficientaerobic decomposition temperatures; and precolating releasible moisturethroughout the organic material.
 2. The method of claim 1 wherein thecontainer is a substantially moisture-retentive bag.
 3. The method ofclaim 1 wherein the air-intake means comprises a discharge blower and aseries of conduits extending therefrom, said conduits inserted throughsaid container openings and extending substantially to the bottomportion of the container.
 4. The method of claim 3 wherein the portionsof said conduits inserted into the container are perforated.
 5. Themethod of claim 1 wherein the organic material is aerated at a rate ofabout 400-1100 cubic feet per minute and a static pressure of at least0.5 inches of water.
 6. The method of claim 5 wherein the organicmaterial is aerated at a rate of about 600 cubic feet per minute and astatic pressure of about 0.5-1.5 inches of water.
 7. The method of claim1 wherein the organic material includes a bulking agent.
 8. The methodof claim 7 wherein the bulking agent is about 10-70 percent by weight ofthe organic material.
 9. The method of claim 8 wherein the bulking agentis about 25-50 percent by weight of the organic material.
 10. The methodof claim 1 wherein the organic material is packed with a pressure ofabout 0.5-5.0 pounds per square inch.
 11. The method of claim 10 whereinthe packed organic material has a density of about 25-35 pounds percubic foot.
 12. The method of claim 1 wherein percolation involvesrelease of said moisture content from the organic material duringdecomposition, vaporization of the same by heat generated thereby, andcondensation on the container.
 13. The method of claim 1 furthercomprising monitoring the internal temperature of said organic materialto determine the aeration rate required for optimal decomposition. 14.The method of claim 1 further comprising injecting water into saidorganic material to achieve optimal decomposition.